The invention relates to an article of manufacture (also referred to as a workpiece), particularly a housing for an electrical switch. First and second plastic parts of the article of manufacture are in a face-to-face relationship and are welded together by a laser beam along a joining zone. The first and second plastic parts have, for a laser beam spectrum, transmission coefficients as well as absorption coefficients different from one another. The first plastic part has a first coupling-in zone designed as a location of impingement of the laser beam. The first plastic part is transparent for the laser beam from the first coupling-in zone to the joining zone, whereby at least one part of the laser beam can pass through the first plastic part and can penetrate into the second plastic part at a second coupling-in zone thereof. The second plastic part is absorbent for the laser beam in a region of the joining zone at the second coupling-in zone. The invention also relates to a process of welding together the first and second plastic parts by a laser beam to form the article of manufacture.
Housings consisting of plastic for electrical switches serve for accommodating the electrical components, such as fixed contacts, switching contacts, etc., and possibly further components. The housings are generally composed of a plurality of housing parts, as a rule of a complex spatial shape. The housing parts are put together during the assembly of the switch, a solid connection between the housing parts often having to be produced. This connection must be adapted to the contour of the housing parts and consequently may have a spatially three-dimensional form.
It is known, in particular if the housings are to be hermetically sealed toward the outside, to connect the housing parts to one another by means of ultrasonic welding. It is disadvantageous in this case that solder connections on the electrical components and also the electrical components themselves may be destroyed on account of the ultrasonic vibrations, ultimately making the switch unusable. There is consequently the need for a process for welding the housing parts of electrical switches which does not adversely affect the electrical components.
It is known from German Offenlegungsschrift 36 21 030 to weld plastic films to one another by the action of laser beams. For this purpose, the plastic films are laid flat one on top of the other. Subsequently, a focused laser beam passes through the films, the films being heated in the joining zone in such a way that they assume a molten state, with the result that after cooling they are bonded together in the joining zone.
Films are thin parts, with the result that heating up in the entire joining zone is possible when the laser beams pass through. As a rule, an acceptable welded connection between the films is thereby accomplished. In the case of thicker workpieces, such as in the case of housings of electrical switches, only a superficial heating up of the workpiece is possible however with the known joining process, whereby a usable welded connection between two workpiece parts is not achievable. In particular, for design reasons, in the case of housing parts of electrical switches the joining zone is often arranged on the inner side of the housing. Such an inner welded connection obviously cannot be produced by the known joining process.
A process for welding sheets of plastic by means of laser beams is further known from EP-A2-0 159 169. In the case of this process, a second sheet is arranged on a first sheet, which is made to be absorbent for the laser beam by using an additive in the plastic. Used as the additive is a black dye, in most cases carbon black. The plastic of the second sheet does not contain any additives, with the result that the second sheet is largely transparent for the laser beam.
Subsequently, a laser beam acts on the second sheet, the laser beam penetrating the second sheet and being absorbed in the first sheet, with the result that the contact surfaces of the two sheets adjacent to one another melt and bond together during the subsequent cooling.
In the case of this process it is disadvantageous that the second sheet must not contain any additive and is in an uncolored, milky-white state, while the first sheet is colored with a black dye. The workpieces produced thereby are consequently composed of parts of a very different color, with the result that the overall visual impression is adversely affected. It is, however, desired specifically in the case of housings of electrical switches that the complete housing has a homogeneous visual impression, in particular with regard to the color. Moreover, the sheets shown in the published specification constitute planar formations which are welded together over a flat surface. However, as a rule, housing parts, in particular those for electrical switches or the like, have complicated geometries, the joining zone of the parts to be connected to one another having to follow this geometry and therefore not being restricted to one plane. The published specification does not provide any suggestion for the production of complex, spatially extending joining zones. The known process is therefore not suitable for the welding of housing parts, in particular for electrical switches.